Molding machines currently exist which utilize a vacuum chamber to aid in the molding process. An example of such a press is disclosed in U.S. Pat. No. 4,666,551, which is hereby incorporated by reference. These types of machines have been used typically to produce low volumes of molded products and/or multi-layer circuit boards. When used to produce molded products, mold cavities are filled with "preforms" by the operator. The press closes and the molding chamber is evacuated. The products are then molded while being subjected to vacuum, heat and mechanical clamping forces exerted by the mold halves.
Vacuum techniques have also been tried in an effort to improve injection molding. In the past, specialty vacuum molds having discharge ports have been created to remove air from the cavity. These special vacuum molds can be very expensive and the ports are subject to plugging which ultimately causes degradation of the molded product.